This invention relates to a process of producing a color selection mechanism for a cathode-ray tube such as a color television image receiving tube and/or a color display apparatus.
A typical conventional color cathode-ray tube is shown in a diagrammatic cross-sectional view of FIG. 1. Referring to FIG. 1, a cathode-ray tube body 1 includes a panel section 1P, a funnel section 1F. and a neck section 1N. The panel section 1P has a panel 2a having a color fluorescent screen 3 formed on an inner face of the panel 2a, and a skirt 2b formed in an integral relationship with and extending from a periphery of the panel 2a to the funnel section 1F and having an end face secured by fritting to an end face of an opening of the funnel section 1F. A color selection electrode 4 having a plurality of electron beam-passing openings 4a perforated therein, such as, for example, a shadow mask, is disposed within the pannel section 1P in an opposing relationship to the color fluorescent screen 3 formed on the inner face of the panel 2a so that, for example, three electron beams R, G and B corresponding to red, green and blue colors, respectively, may land on corresponding fluorescent patterns for the respective colors on the color fluorescent screen 3. Reference numeral 7 denotes means for deflecting the electron beams R, G and B in horizontal and vertical directions.
The color selection electrode 4, for example, a shadow mask, is normally produced by perforating a great number of openings such as round holes or elongated holes in rows and columns in a cold rolled steel plate material of a thickness of 0.08 to 0.35 mm using a photochemical process. Such a process comprises photolithography and then stamping, (drawing) the steel plate into a required facial shape, that is, a shape corresponding to the shape of the curved face of the panel 2a of the cathode-ray tube body, and generally into a segmental spherical shape. The color selection mechanism 6 is constructed by welding a periphery of the color selection electrode 4 to a support frame 5.
However, when a color selection electrode is to be produced by stamping a metal plate material in this manner, an annealing operation is required to process the metal plate material at a temperature of 850.degree. C. to 950.degree. C. within a reducing atmosphere prior to such stamping so that a possible elongation by 1 to 3 per cent of the metal plate material, which will occur upon such stamping, may not cause fracture of the metal plate material, particularly at bridging portions between adjacent openings. Further, an additional operation is required to remove any yielding point elongation of the metal plate material caused by the annealing, by passing the metal plate material between roller levellers. After those operations, the stamping operation is performed. Thus, the prior process of production is very complicated (refer to a magazine "Iron and Steel", No. 2 of 1981, pp. 65-70).
Further, this process involves a problem of the homogeneity of a material of a metal plate itself. In particular, where there is some component segregation in a metal plate material, elongation upon stamping will not be uniform so that an uneven change in shape may appear around openings of the metal plate material, resulting in uneven transmittivity of electron beams. Since such unevenness of the material of a metal plate becomes clear after stamping, that is, after several steps such as annealing and levelling steps, production loss is significant. Besides, if crystal grains are too large after annealing, an uneven transmittivity of electron beams will be caused by stretcher strains. Therefore, elaborate and expensive examination of material lots becomes necessary.
Moreover, where the above process is employed, it is necessary in inital design to anticipate changes in the dimension and pitch of openings due to elongation of the material upon stamping. Thus, unstable elements are prominent. Further, upon designing openings, it is necessary to take into consideration a provision for avoiding appearance of a moire pattern due to an interference between so-called bridging portions between openings and a scanning line. Accordingly, designing of a color selection mechanism will be complicated by consideration of changes in pitch and shape of openings as described above.
In addition, in designing the segmental spherical face of such a color selection electrode, considerations of spring-back thereof will be necessary. In particular, when a metal plate material is drawn into a segmental spherical shape by stamping, it is deformed within a plastic region beyond the elastic limit thereof, and after such plastic deformation, an elastic restoration, that is, a spring-back, will appear. Accordingly, if stamping using a metal mold having, for example, a radius of curvature R is considered, the radius of curvature of an electrode finally produced produced will be R+.DELTA.R which is greater by .DELTA.R than the desired radius of curvature R. Accordingly, in order to finally obtain an electrode which has a segmental spherical face having a radius of curvature R, a metal mold for stamping it must necessarily be previously corrected for its radius of curvature involving such a spring-back as described above. Commonly, a metal mold is corrected or modified several times before an electrode having a face of a desired radius of curvature can be produced by stamping with the metal mold. Such corrections or modifications of a metal mold are very troublesome. Besides, since a degree of a spring-back will vary also depending upon variations in composition of the metal plate material, it is very difficult and troublesome to obtain a color selection mechanism of desired dimensions and a desired shape with consistent accuracy.
Meanwhile, patterns of fluorescent materials for individual colors in the form of dots or stripes which form a color fluorescent screen in a color cathode-ray tube are required to be disposed as uniformly as possible on an inner face of a panel 2a of the cathode-ray tube. Individual beams R, G and B are thus required to be selected by a color selection mechanism and landed respectively on the fluorescent materials of the corresponding colors. Separate applications of fluorescent patterns of individual colors on an inner face of a panel 2a are achieved using a well-known process that slurries of the fluorescent materials containing a photosensitive bonding agent are applied to an inner face of a panel, and then a color selection mechanism is mounted in position in an opposing relationship on the panel whereafter paths of electron beams are replaced by light to optically print the slurries of the fluoresent materials of the individual colors one after another using the actual color selection mechanism, or shadow mask as the light exposure mask.
As described above, in order to attain equal arrangements of fluorescent materials of individual colors, that is, in order to attain a condition appropriate for allowing individual electron beams R, G and B to be equally landed on the fluorescent materials of the respective colors, a color selection electrode 4 and a panel 2a must necessarily be arranged in a predetermined relationship.
Generally, there are two types of panels for color cathode-ray tube bodies: one is segmental spherical in its basic facial shape, and the other is cylindrical. Thus, in order to arrange a color selection electrode 4 and a panel 2a in an appropriate relationship to equalize arrangements of individual colors as described above, where a color selection electrode 4 is segmental spherical, preferably a segmental spherical panel 2a is used in combination. On the other hand, where a color selection electrode 4 is cylindrical, preferably a cylindrical panel 2a is used in combination.
A variation of color selection electrodes 4 of the cylindrical type has openings for passing electron beams which are formed as slits extending in a parallel relationship over the full vertical extent of an effective picture area. In the variation, a color selection electrode having slits formed therein is welded at opposite edges thereof in the extending direction of the slits to a pair of sides of a support frame which are curved along a cylindrical face of the frame so as to mount the color selection electrode in tension in a cylindrically curved condition on the support frame without involving a drawing operation as described above. While such troublesome operation as an annealing operation accompanying a stamping operation of a levelling operation as described above can be avoided with such a construction, since the color selection electrode is kept in tension thereby, the shape of the color selection electrode in the direction of the tension is limited to one which has a completely infinite radius of curvature, that is, to a straight one, which restricts the degree of freedom in designing. As a result, a panel section of a tube body which is used in combination with the color selection electrode of the construction described is also restricted in dimension and shape. Such restrictions will now be described. It is known that an appropriate distance L.sub.SG between an electrode 4 and a panel 2a for attaining appropriate arrangements of fluorescent material patterns of individual colors as described above, or in other words, an appropriate arrangement of landing positions on a panel 2a of electron beams R, G and B corresponding to the respective colors determined by a color selection mechanism, is given by an equation ##EQU1## where S.sub.D is a distance, where three electron beams R, G and B corresponding to red, green and blue are arranged, as viewed from the side of the panel 2a as seen in FIG. 1, in a horizontal straight line, between the centers of deflection P.sub.C and P.sub.S of a beam which is positioned centrally of the three electron beams R, G and B and the other beams positioned on opposite sides of the central beam, P.sub.G is a pitch of openings, and L.sub.S is a distance between the center of deflection P.sub.C and the fluorescent screen 3, and wherein L.sub.S and S.sub.D vary depending upon deflection of an electron beam. Thus, if the requirement of the equation (1) is met over the entire area of the fluorescent screen 3, landing positions of the three beams R, G and B are appropriately arranged over the entire area of the fluorescent screen 3.
Now, if landing positions L.sub.P R, L.sub.P G and L.sub.P B of beams R, G and B on the fluorescent screen 3 controlled by the openings 4a of the color selection electrode 4, exhibit an appropriate arrangement as seen in FIG. 12A, where a distance between the panel 2a and the electrode 4 has a relation as seen in FIG. 12B, the landing postiions L.sub.P R, L.sub.P G and L.sub.P B show a degrouping which expands at a corner portion of the fluorescent screen 3 as seen in FIG. 13A in case the radius of curvature of the panel 2a is large as shown in FIG. 13B, but in case the radius of curvature of the panel 2a is small as shown in FIG. 14B, an excessive grouping appears at a corner portion of the fluorescent screen 3 as seen in FIG. 14A. Actually, there may be some differences depending upon the pitch of openings or slits 4a of the color selection electrode 4, the deflection angle, the beam space of electron guns, and specification of deflecting means 7, but if it is intended to obtain patterns of fluorescent materials in the form of appropriately arranged stripes using a color selection electrode having a perfectly cylindrical face as described above, the shape of the panel 2a will be such that, for example, if a horizontal direction on a plane of the panel 2a is designated a direction of x axis, a vertical direction is designated a direction of y axis and a direction of the central axis is designated a direction z axis, the radius of curvature R.sub.pyo in the y direction across the z axis and the radius of curvature R.sub.pys of opposite sides positioned in parallel to the same having a relation EQU R.sub.pys &lt;R.sub.pyo ( 2)
while the radius of curvature R.sub.pxo in the x direction across the z axis and the radius of curvature R.sub.pxs of opposite sides positioned in parallel to the same having a relation EQU R.sub.pxs &lt;R.sub.pxo ( 3)
In fact, errors in dimension of a color selection electrode are small and an error in pitch P.sub.G is also small. Further, errors of the distance L.sub.S between the deflection center P.sub.C of a beam and the fluorescent screen 3 and the distance S.sub.D between the deflection center P.sub.C of the central beam and the deflection centers P.sub.S of the beams on both sides are small, and hence what matters more is an error due to variations of the radius of curvature of the glass panel. However, a panel section 1P is produced by molding a glass material which is molten at a high temperature, and in this case, since the radius of curvature and shape of panels 2a will vary, for example, with each lot, depending upon various conditions such as the temperature of glass and the cooling time will be selected in accordance with dimensions, resulting in lowering of production.
As described above, according to conventional processes of producing a color selection mechanism, when a segmental spherical color selection electrode is to be produced, a complicated production process is required. On the other hand, when a perfectly cylindrical color selection electrode is to be produced, a complicated adjustment of the shape of an inner face of a panel or selection of panel is necessary.